1. Technical Field of the Invention
The present invention relates to the administration of C-glycoside compounds for depigmenting and/or whitening the skin.
2. Description of Background and/or Related and/or Prior Art
The color of human skin depends on various factors, in particular on the seasons of the year, race and sex, and it is mainly determined by the nature and the concentration of melanin produced by the melanocytes. Melanocytes are specialized cells which synthesize melanin via specific organelles, the melanosomes. In addition, at different periods in their lives, certain individuals witness the appearance on the skin and more especially on the hands of darker and/or more highly colored blemishes which give the skin a heterogeneous appearance. These blemishes are also due to a high concentration of melanin in the keratinocytes situated at the surface of the skin.
The use of inoffensive topical depigmenting substances which are highly effective is very particularly sought with a view to treating regional hyperpigmentations by melanocytic hyperactivity, such as idiopathic melasmas, arising during pregnancy (“mask of pregnancy” or chloasma) or oestrone/progestogen contraception, localized hyperpigmentation by benign melanocytic hyperactivity and proliferation, such as senile pigment blemishes known as actinic lentigines, accidental hyperpigmentations, possibly due to photosensitization or to post-lesional healing, as well as certain leucodermas, such as vitiligo. For the latter conditions (healing of which can result in a scar giving the skin a whiter appearance), for want of being able to repigment the damaged skin, the end result is to depigment the remaining normal skin regions to give the whole skin a homogeneous white coloring.
The mechanism of formation of the pigmentation of the skin, that is to say of the formation of melanin, is particularly complex and involves, schematically, the following main stages:                Tyrosine→Dopa→Dopaquinone→Dopachrome→Melanin        
Tyrosinase (monophenol dihydroxyl phenylalanine:oxygen oxidoreductase EC 1.14.18.1) is the essential enzyme involved in this sequence of reactions. In particular, it catalyzes the conversion reaction of tyrosine to give Dopa (dihydroxyphenylalanine), by virtue of its hydroxylase activity, and the conversion reaction of Dopa to give dopaquinone, by virtue of its oxidase activity. This tyrosinase only acts when it is in the maturation state under the effect of certain biological factors.
The depigmenting substances can act directly on the vitality of the epidermal melanocytes where melanogenesis takes place and/or interfere with one of the stages in the biosynthesis of melanin, either by inhibiting one of the enzymes involved in melanogenesis or by being inserted as structural analogue of one of the chemical compounds in the sequence for the synthesis of melanin, which sequence can then be blocked and thus ensure depigmentation.
The substances most commonly used as depigmenting agents are more particularly hydroquinone and its derivatives, in particular its ethers, such as hydroquinone monomethyl ether and monoethyl ether. These compounds can, however, produce undesirable effects, such as the appearance of red skin blotches, in specific situations, such as use at high concentrations, sensitive skin or skin exhibiting a dermatological disorder, and the like.
Furthermore, use is commonly made, as inhibitor of the activation of tyrosinase, of kojic acid, which complexes the copper present in the active site of this enzyme. However, this compound can prove to be unstable in solution, which complicates its formulation.
Thus, need continues to exist for novel whitening agents for human skin with an action as effective as those known to the art and which are non-irritating, non-toxic and/or non-allergizing for the skin while being stable in a composition, or else alternatively which have a reinforced action, so as to be able to be administered in a smaller amount, which greatly reduces any side effects.